Much attention has been given in recent years to systems used in retail stores for displaying goods prices. While manual marking of the prices at the location of the goods, or on the goods themselves, is conventional, attempts have been made to use electronic means, instead, for displaying the prices at the goods location.
Some electronic price display systems have been proposed to employ electronic labels or modules, each typically having a liquid crystal display, for displaying the prices. Buses for power and data are used in such systems to connect many thousands of such labels to a central computer for the latter to communicate with particular ones of the labels to, for example, request changes in their displayed prices. To this end, the labels are equipped with connectors so that they can be snapped onto one of many locations along rails which include the buses and which run along the edges of the store shelves. The connectors also provide the labels with electrical connections to the central computer through the buses.
Experience has shown that physical placement of products within a store has, oftentimes, enormous influence on the sales of the products. Factors including shelf height and the number of product facings along a shelf can be of great significance to store planners. Thus, it is important for a store planner to ensure that the "plan-o-gram" of the store, which is a plan showing product locations on shelves, is faithfully adhered to. However, deviations from the plan-o-gram could often result from accidental or intentional misplacement of the labels by store personnel, customers or others.
A scheme has been proposed for detecting such misplacement by monitoring power outage of the labels, assuming that a misplaced label has been removed from its power before relocated. Undesirably, such a proposed scheme is not capable of detecting displacement of a label along the rail without interrupting its power. A fortiori, it is not capable of determining the location of the displaced label.